Poly(arylene ether) resins have been modified with polyamide resins to provide a wide variety of beneficial properties such as heat resistance, chemical resistance, impact strength, hydrolytic stability, and dimensional stability compared to either unmodified resin alone. When a conductive agent, such as conductive carbon black, is incorporated into poly(arylene ether)/polyamide (PAE/PA) compositions, electrically conductivities suitable for electrostatic painting may be achieved.
A variety of methods have been described for preparing conductive PAE/PA compositions. U.S. Pat. No. 5,843,340 to Silvi et al. generally describes preparation of conductive PAE/PA compositions having excellent ductility by melt blending polyphenylene ether, an unsaturated impact modifying polymer and a functionalizing compound in an initial step, optionally in combination with a portion of the polyamide, and subsequently melt blending with the remainder of the polyamide and conductive carbon black having a low volatiles content.
U.S. Pat. No. 5,977,240 to Marie Lohmeijer et al. generally describes a thermoplastic composition comprising (a) a compatibilized PAE/PA base resin, and (b) 1-7 parts by weight per 100 parts by weight of (a) of an electroconductive carbon black. The composition is prepared by first forming the compatibilized PAE/PA base resin, then adding the electroconductive carbon black.
U.S. Pat. No. 6,171,523 to Silvi et al. generally describes a method for the preparation of conductive PAE/PA compositions having excellent ductility, the method comprising melt blending polyphenylene ether, an unsaturated impact modifying polymer and a functionalizing compound in an initial step, optionally in combination with a portion of the polyamide, and subsequently melt blending with the remainder of the polyamide and conductive carbon black having a low volatiles content.
U.S. Pat. No. 6,221,283 to Dharmarajan et al. generally describes a method of making a conductive thermoplastic composition containing at least one dispersed phase polymer with a continuous phase polymer and at least one conductivity imparting agent wherein the bulk resistivity of the composition is at least partially determined by the particle size of the dispersed phase within the continuous phase. The thermoplastic composition preferably comprises a compatibilized blend of at least one polyphenylene ether resin, at least one polyamide resin, and at least one conductivity imparting agent, and optionally, one or more of impact modifiers, stabilizers, antioxidants, lubricants, and fillers.
PAE/PA compositions are typically manufactured using a single-screw or twin-screw extruder characterized by a screw length and a screw diameter. Existing manufacturing methods for PAE/PA compositions having desirable properties typically require an extruder having at least twelve barrels and a screw length to diameter ratio of at least 40. Such extruders require so much space that it is difficult to accommodate them in many manufacturing facilities. There is a need for a PAE/PA preparation method that allows the use of more compact extruders.
The above-described and other drawbacks and disadvantages are alleviated by a method of preparing a conductive thermoplastic composition, comprising: adding to a first feed port of an extruder about 20 to about 70 parts by weight of a poly(arylene ether) and 0 to about 20 parts by weight of a first polyamide; adding to a second feed port of the extruder about 20 to about 75 parts by weight of a second polyamide, wherein the second feed port is downstream of the first feed port; and adding to the second feed port or a third feed port of the extruder about 5 to about 40 parts by weight of a concentrate comprising about 5 to about 20 weight percent of a conductive carbon black and about 80 to about 95 weight percent of a third polyamide, wherein the third feed port is downstream of the second feed port; wherein the extruder has a screw length to diameter ratio less than 38.
Other embodiments, including methods utilizing particular poly(arylene ether) and polyamide resins, and methods utilizing additional components in the conductive thermoplastic composition, are described in detail below.